Avariation of a language found in a geographically isolated area is a(n)
ethnic dialect
social dialect
regional dialect

A variation of language found in a geographically isolated area is called regional dialect. Dialect is a word meaning a variety of language that signals where a person comes from. Dialect is usually interpreted geographically (regionally) hence the term regional dialect. A dialect is distinguished from other dialects of the same language mainly by features of linguistic structure such as grammar (specifically morphology and syntax) and vocabulary. For example wheat known by that name in England while in Scotland it is known as oats. Corn is known by that name in England while in America it is known as maize.